# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def FindKthToTail(self, head, k):
        slow , fast = head , head
        for i in range(k):
            if fast == None:
                return None
            fast = fast.next
        while fast:
            fast = fast.next
            slow = slow.next
        return slow